JSON strings to collection Java

Question

I have JSON string

For Example

[{  
 "id":"abc",
 "name":"ffa",
 "done":0
},
{  
 "id":"abc",
 "name":"ffa",
 "done":0
}]

I want to convert this JSON to collection of Examp class. I've tried use gson.

public static void main(String[] args)
{
   Gson gson = new Gson();
   Examp a=new Examp(); //Class Examp have 3 fields (id,name,done)
   Examp b=new Examp();

   a.done=0;
   b.done=0;

   a.id="foo";
   b.id="foo1";

   a.name="faa";
   b.name="faa1";

   ArrayList<Examp> arr= new ArrayList<Examp>();
   arr.add(b);
   arr.add(a);

   String str = gson.toJson(arr);
   System.out.println(str); //format check

   ArrayList<Examp> collection = gson.fromJson(str, ArrayList.class);

}

At this moment the type of data in collection isn't Examp, but LinkedTreeMap. I have one question. How can I access this data (for example name)?

Answer 1

You need a TypeToken

ArrayList<Examp> collection = gson.fromJson(str, new TypeToken<ArrayList<Examp>>(){}.getType());

The TypeToken is kind of a generic hack to get the generic type argument of a generic type use.

Note that you won't be able to use TypeToke with type variables. (You'll be able to use it, but won't get what you want/expect).

Answer 2

You need to use TypeToken:

Type type = new TypeToken<ArrayList<Examp>>() {}.getType();
List<Examp> collection = gson.fromJson(json, type );

Reference on their wiki page: